The invention relates to closed xcex94Pstat equipment for the potential-independent control of the pressure gradient for investigations of flow through columns under a high hydrostatic pressure as well as to a method for controlling differential pressure and can be used especially for carrying out migration investigations in pressure columns.
The planning and selection of suitable methods for cleaning up the environment in many cases takes place after extensive investigations on soil and water samples in the laboratory. Dynamic migration experiments in column equipment, which simulates the transport processes, exchange processes and conversion processes in the underground, provide important information for this. They enable cause and effect relationships to be analyzed, so that, for example, the processing of subterranean water or the cleaning up of old polluted areas can frequently be configured optimally with relatively little expense.
When flow and migration processes are simulated in coarse media at high hydrostatic pressures, for example, for describing the migration of pollutants in deep or immense aquifers, the following problem arises: a sufficiently fine harmonization of differential pressures (for example: 1 . . . 200 mbar) and the maintaining of these differences constantly fails at high surrounding pressures (such as 1 . . . 10 bar) as a result of the response accuracy and the switching hysteresis of technical pressure regulating devices.
However, an understanding of migration under extreme pressure conditions can effectively be developed further only if fluids can be driven through porous media at fixed hydrostatic pressures and hydraulically effective pressure gradients within enveloping materials and determined gas composition of fluid (oxygen-free).
The principal of the potential bottle, with which a lamella of fluid (drawn bright) having a height of xcex94h=h2xe2x88x92h1 is held above the atmospheric pressure Patm (see FIG. 2), is known. By pulling the small air tube by dh2, the height of the fluid in the open vessel is raised by the same amount dh2. At the same time, the equivalent volume of air flows through the small air tube and collects in the bottle.
The reason for this behavior is as follows. An equipotential surface with the pressure P(h2)=Patm is formed within the bottle at the height of the air outlet point of the small tube h2 and is maintained by the liquid lamella and air lamella, which are above this equipotential surface and are in equilibrium with atmospheric pressure.
The British patent 2,218,992 A discloses an industrial volume-flow control system, which is to attain a uniform flow through the HPLC column, particularly in the event that the column is built up inhomogeneously. The volume flow on either side of the column and, with that, also at every cross-sectional site within the column, is kept constant here by the controlled addition at the inlet and the controlled removal of solvent at the outlet. The volume flow is controlled by the uniform and oppositely directed change in the solvent volume in the solvent reservoir bottles disposed about the column, the volume change being controlled over a membrane by the volumetric ratio of a working fluid to the bottle volume. Synchronized, oppositely running pumps are used for the control.
Disadvantages of this solution are the relatively high technical effort with active control and regulating components, as well as the separation of the working fluid from the elution fluid by an elastic membrane.
Utilizing this principle, it is an object of the invention to provide equipment and a method for carrying out column investigations under pressure, with which differential pressures can be harmonized finely and maintained constantly independent of external influences, such as air pressure, air pressure changes, air composition and temperature. Moreover, it shall be possible to manufacture the equipment cost effectively and to operate and maintain it easily.
Pursuant to the invention, this objective is accomplished by the distinguishing features in the characterizing part of claims 1, 6 and 7 in conjunction with the distinguishing features in the introductory portion.
Appropriate developments of the invention are contained in the dependent claims.
A particular advantage of the invention consists therein that the pressure and differential pressure are independent of external influences, such as the composition of the air, any changes in air pressure and the temperature, etc. This is achieved owing to the fact that a closed system of vessels, consisting of at least one column, at least one start potential bottle and at least one target potential bottle, is acted upon with a uniform pressure, and the differential pressure for moving the fluids through the column is produced by the difference between the heights of the fluid in the start potential bottle and the target potential bottle according to the equation
xcex94hw=hBxe2x88x92hA with xcex94Pstat=xcfx81fluidg xcex94hw
wherein
xcex94hw xe2x80x94is the effective fluid height difference
hA xe2x80x94is the potential height of the fluid in the start potential bottle
hB xe2x80x94is the potential height of the fluid in the target potential bottle
xcex94Pstat xe2x80x94is the stationary pressure gradient
xcfx81fluid xe2x80x94is the fluid density
g xe2x80x94is the acceleration due to gravity.
The magnitude of the pressure, which can be applied for the simulation of a corresponding hydrostatic pressure, depends only on the technical realization of the system and is designed depending on the objective set. The magnitude of the pressure is not determined by the position or accuracy, with which the differential pressure can be set. Instead, this differential pressure is determined only by the resulting fluid height difference xcex94hw and the accuracy only by the reading error when xcex94hw for fluids of a given density is determined, in that at least one start potential bottle is coupled with at least one target potential bottle into a closed system of vessels in such a manner, that a difference between the height of the fluid in the start potential bottle and that in the target potential bottle can be set and the fluid outlet of the start potential bottle is connected with the column inlet and the fluid inlet of the target potential bottle is connected with the column outlet over at least one fluid line and the pressure inlet of the start potential bottle is connected with the pressure inlet of the target potential bottle over at least one pressure line, which is acted upon by one pressure medium.
For higher accuracy requirements, xcex94hw can be determined directly through the use of sight glasses, which can be mounted on the potential bottles. (Sight glasses can also be used to check the level to which the potential bottles are filled.) Indirectly, an accurate potential equalization is possible by setting the potential difference, at which the fluid transport between at least two (short-circuited) potential bottles barely ceases, equal to zero
xcex94hw=0
As fluids, any combination of liquids, capable of forming drops, or gases can be used, which must be unmiscible with one another and have a sufficient density difference. The pressure system can be uncoupled at any time from the sediment-filled column. Valves and optionally self-closing couplings ensure the contamination-free coupling and uncoupling of the system.
By selecting suitable materials and compressed gases, interactions between the technical system and the fluids to be investigated can be precluded for the specific case.